From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752525AbeEPNbg (ORCPT ); Wed, 16 May 2018 09:31:36 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:57984 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752309AbeEPNbe (ORCPT ); Wed, 16 May 2018 09:31:34 -0400 Subject: Re: [RFC v4 4/5] virtio_ring: add event idx support in packed ring To: Tiwei Bie Cc: mst@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, wexu@redhat.com, jfreimann@redhat.com References: <20180516083737.26504-1-tiwei.bie@intel.com> <20180516083737.26504-5-tiwei.bie@intel.com> <64f5085b-4b62-d545-36e0-0951c11b29a8@redhat.com> <20180516125825.GA4171@debian> From: Jason Wang Message-ID: Date: Wed, 16 May 2018 21:31:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180516125825.GA4171@debian> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018年05月16日 20:58, Tiwei Bie wrote: > On Wed, May 16, 2018 at 08:17:21PM +0800, Jason Wang wrote: >> On 2018年05月16日 16:37, Tiwei Bie wrote: > [...] >>> @@ -1160,15 +1186,27 @@ static void virtqueue_disable_cb_packed(struct virtqueue *_vq) >>> static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) >>> { >>> struct vring_virtqueue *vq = to_vvq(_vq); >>> + u16 wrap_counter; >>> START_USE(vq); >>> /* We optimistically turn back on interrupts, then check if there was >>> * more to do. */ >>> + /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to >>> + * either clear the flags bit or point the event index at the next >>> + * entry. Always update the event index to keep code simple. */ >>> + >>> + wrap_counter = vq->wrap_counter; >>> + if (vq->last_used_idx > vq->next_avail_idx) >> Should this be ">=" consider rx refill may try to completely fill the ring? > It seems that there are two cases that last_used_idx > equals to next_avail_idx. The first one is that the > ring is empty. And the second one is that the ring > is full. Although in the first case, most probably, > the driver won't enable the interrupt. > > Maybe I really should track the used_wrap_counter > instead of calculating it each time I need it.. I'll > give it a try.. > Right, good to know and this will match spec sample code. Thanks